This invention relates to a Multi-layer padding welding method.
Welding robots are currently being developed extensively for the labor savings in welding operations, improvement in quality, improvement in environmental conditions of welders, etc. Multi-layer padding is one of the very important functions of welding operations where welding robots are employed, but it is technically difficult.
For performing multi-layer welding by a welding robot, the first layer welding path is taught first, and then the second, the third (and so forth) layer welding paths are sequentially taught. The paths of the second and subsequent layers should be taught taking the welding conditions of up to the previous layer into consideration, and as a result the center-to-center distance between the layers becomes uneven, lowering the welding accuracy.
As shown in FIG. 1, when double layer padding (groove welding) of members 5 and 6 shown in FIG. 2 is performed by a welding robot having welding torches 1 and 2, ends of welding wires 3 and 4 of the torches 1 and 2 are caused to extend toward the weld line for lengths differing by .DELTA..sub.L2 with each other and to be mutually spaced by .DELTA..sub.L1, and then the torch 1 is taught to follow the welding path of the first layer. As the torch 1 moves from the weld start point P for the distance of .DELTA.L.sub.1 while welding the first layer, the torch 2 starts welding the second layer at the point P. When the above double layer padding is viewed from the weld line, the distance between the weld center C.sub.1 of the first layer and the weld center C.sub.2 of the second layer is equal to the offset .DELTA.L.sub.2 between the ends of welding wires 3 and 4 of the welding torches 1 and 2. Accordingly, the center-to-center distance of welding between layers becomes uniform, enabling high accuracy welding.
However, this system is expensive due to the necessity of two (or more) welding torches, and the center-to-center distance .DELTA.L.sub.2 of welding cannot be changed easily. In the case that .DELTA.L.sub.2 is set mechanically, gaining the accuracy of that .DELTA.L.sub.2 is difficult, and change of the values of .DELTA.L.sub.2 requires considerable time, while if .DELTA.L.sub.2 is set electrically or hydraulically, a servo mechanism is required for positioning, boosting the price. Furthermore, there is a problem that this method cannot be applied to multi-layer padding of a fillet weld as shown in FIG. 4.